Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: xersanozgen on 22/09/2017 13:04:04
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When will the Sun's and Andromeda's photons meet?
Two photons (which have been emitted from the Sun and Andromeda on the same moment To) approach to each other.
The distance to the Andromeda Galaxy is 2.54 million light-years.
When will these photons meet? Tı = ?
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The midpoint would be 1.27 million light years. You cannot simply state that this is the point that they meet since a) the universe is expanding and b) there could be forces present along the photon paths that could deflect them. These are just two of the complications that could throw out any calculation.
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The Sun is thought to be about 4.5 billion years old.
A (younger) Andromeda galaxy would have existed well before that.
So photons from both would have passed each other about 4.5 billion years ago.
Andromeda is approaching our Milky Way galaxy; they are expected to collide in about 5 billion years.
So we could assume that they were about 5 million light-years apart at the time of the Sun's formation.
Photons from Andromeda would have been "in flight" for at least 5 million years prior to the Sun's formation, so the photons from the Andromeda galaxy would have reached the Sun as soon as the Sun burnt its way out of the dust cloud in which it formed.
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The midpoint would be 1.27 million light years. You cannot simply state that this is the point that they meet since a) the universe is expanding and b) there could be forces present along the photon paths that could deflect them. These are just two of the complications that could throw out any calculation.
Is 1.27 million light years or merely 1.27 million years?
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The Sun is thought to be about 4.5 billion years old.
A (younger) Andromeda galaxy would have existed well before that.
So photons from both would have passed each other about 4.5 billion years ago.
Andromeda is approaching our Milky Way galaxy; they are expected to collide in about 5 billion years.
So we could assume that they were about 5 million light-years apart at the time of the Sun's formation.
Photons from Andromeda would have been "in flight" for at least 5 million years prior to the Sun's formation, so the photons from the Andromeda galaxy would have reached the Sun as soon as the Sun burnt its way out of the dust cloud in which it formed.
To = the moment of starting to travel for the Sun's and Andromeda's photons = now
Tı = the colliding or meeting moment = ?
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Is (it) 1.27 million light years or merely 1.27 million years?
Both.
In a vacuum, light travels at "the speed of light".
- So in space, light travels 1 light-year in 1 year.
- And 1.27 million light years in 1.27 million years
If you look at photons emitted now by the Sun and Andromeda, they will pass at the half-way point, which is 1.27 million light years away, in 1.27 million years.
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The midpoint would be 1.27 million light years. You cannot simply state that this is the point that they meet since a) the universe is expanding and b) there could be forces present along the photon paths that could deflect them. These are just two of the complications that could throw out any calculation.
The latest expansion rate measurement is about 71.9 kilometers per second per megaparsec. Since the Andromeda is 0.78 megaparsecs away, we'd expect the expansion rate to be about 56 kilometers per second between our two galaxies. Over a period of 1.27 million years, they'd only increase in distance from each other by about 237 light-years, an increase of less than 0.02 percent. So although it's true that the distance would change over that period of time, it's only a very small amount.
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You cannot simply state that this is the point that they meet since a) the universe is expanding
The cosmic expansion of the universe only applies over cosmic distances. The Andromeda galaxy is part of our "local cluster" of galaxies, which are gravitationally bound, and are not affected by today's cosmic expansion of the universe.
In fact, the Andromeda galaxy is moving towards the Milky Way galaxy at around 110 km/sec.
But as Kryptid calculates, this makes very little difference to the answer.
See: https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision
b) there could be forces present along the photon paths that could deflect them.
There is a low concentration of gas and dust between galaxies, and more within the galaxies, so some light could be absorbed.
- Most of the absorption would occur after the photon hit Earth's atmosphere (think cloudy days).
- There is a slight refraction if the photon hits Earth's atmosphere at an angle
Unlike charged particles (eg cosmic rays), photons are not deflected by the magnetic fields of galaxies.
So, barring a giant mirror between the galaxies, our view of the Andromeda galaxy is pretty clear.
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Is (it) 1.27 million light years or merely 1.27 million years?
Both.
In a vacuum, light travels at "the speed of light".
- So in space, light travels 1 light-year in 1 year.
- And 1.27 million light years in 1.27 million years
If you look at photons emitted now by the Sun and Andromeda, they will pass at the half-way point, which is 1.27 million light years away, in 1.27 million years.
Yes, you are right certainly. Thanks.
In that case, the distance between two photons decreases by a value ' 2 c ' of velocity; or the collision speed is 2c.
In CERN, If the particules accelerate up to big fractions of c; the collision speed can be bigger than ' c '.
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The latest expansion rate measurement is about 71.9 kilometers per second per megaparsec. Since the Andromeda is 0.78 megaparsecs away, we'd expect the expansion rate to be about 56 kilometers per second between our two galaxies. Over a period of 1.27 million years, they'd only increase in distance from each other by about 237 light-years, an increase of less than 0.02 percent. So although it's true that the distance would change over that period of time, it's only a very small amount.
Yes, neglectabl.
In my opinion the sources can travel toward anywhere independently*, after emitting a photon packet; so, the distance or travelling way -at the moment of starting for the motion of photons- will be kept by the same value.
* You can see this by using a photo-flash; after flashing you can carry the flash device to anywhere even opposite direction of light.
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https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=71464.0;attach=23974;image
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In that case, the distance between two photons decreases by a value ' 2 c ' of velocity; or the collision speed is 2c.
Relative to an observer, or to each other?
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In that case, the distance between two photons decreases by a value ' 2 c ' of velocity; or the collision speed is 2c.
Relative to an observer *, or to each other?
According to an outmost / co-reference frame (space or Light Coordinate system : LCS)
This analysis is an simple application / example of LCS concept (alternative theory for special relativity). Please read that link:
https://www.thenakedscientists.com/forum/index.php?topic=71218.0 (https://www.thenakedscientists.com/forum/index.php?topic=71218.0)
For detailed analysis of LCS concept and for calculation of universe's age: "Light Kinematics to analyze space-time"
http://adsabs.harvard.edu/abs/2013PhyEs..26...49E (http://adsabs.harvard.edu/abs/2013PhyEs..26...49E)
( * ) 1-The light comes to an observer/receptor by always the speed ' c '; so he can perceive the events ( which are realized by bigger speed than c) in accordance with this condition.
2- If an observer is an actor of analysis and experiment; his visual ability or visual restrictions can cause confusing or incorrect conclusions (our and Einstein's humanly mistake). Therefore we must prefer to use God's eyes for scientific integrity (This is not a new rule).
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In that case, the distance between two photons decreases by a value ' 2 c ' of velocity; or the collision speed is 2c.
There is not actually a collision - the photons pass each other.
Note that photons are massless, and always travel at c, in a vacuum.
In CERN, If the particles accelerate up to big fractions of c; the collision speed can be bigger than ' c '.
Unlike photons, protons have a mass (even at rest), and so can never reach c.
If you work out the collision velocity as seen by one of the protons, the velocity of the oncoming proton is still less than c.
See: https://en.wikipedia.org/wiki/Velocity-addition_formula#Special_relativity
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If you work out the collision velocity as seen by one of the protons, the velocity of the oncoming proton is still less than c.
In CERN, If one of the protons has been accelerated up to 60 % c and the other's 70% c; the collision speed will be 1,30 c . In other words, the distance between these photons decreases by the speed 1,30 c; so, if we assign one of them for reference role, the relative speed of other one must be 1,30 c.
V = (v + w) / (1 + v.w/c²) This formula is valid for genuine relativity (If we throw a rocket from/over another rocket; the speed of relative rocket doesn't exceed the value ' c ').
If the objects get their speed by their own pattern independently ***(that Einstein had ignored this option; but, we can distinguish and internalize the types of relativity), the collision speed must find by additing directly (top limit 2c). In that case radial speeds can get a value up to 2.c
*** For example If we consider two ambulances (which they travel toward each other by their maximum speed); the distance between them decrease by the speed (v + w). We cannot consider the value of maxsimum speed as top limit for the relative speed according to one of them (an ambulance cannot exceed this limit; but the distance can decrease by bigger value than a car's speed.
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If the objects get their speed by their own pattern independently ***(that Einstein had ignored this option; but, we can distinguish and internalize the types of relativity), the collision speed must find by additing directly (top limit 2c). In that case radial speeds can get a value up to 2.c
Radial speed is the escaping speed of sky object from Earth. In fact, it is the total of the vectoral components which the projections of universe expansion speed upon observational line for the Earth and sky object. So, the speeds of two objects are mentioned; therefore the top limit of radial speeds is 2.c .
The theory of SR declared a single c value for the top limit of radial speed. However, its formula (to transform the redshifts) is not correct.
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If the objects get their speed by their own pattern independently ***(that Einstein had ignored this option; but, we can distinguish and internalize the types of relativity), the collision speed must find by additing directly (top limit 2c). In that case radial speeds can get a value up to 2.c
Radial speed is the escaping speed of sky object from Earth. In fact, it is the total of the vectoral components which the projections of universe expansion speed upon observational line for the Earth and sky object. So, the speeds of two objects are mentioned; therefore the top limit of radial speeds is 2.c .
The theory of SR declared a single c value for the top limit of radial speed. However, its formula (to transform the redshifts) is not correct.
The burning phenomen had been wanted to define by Stahl (philogiston theory). This theory had an acceptance like reality for a long time.
Similarly, the theory SR is a first effort for light kinematics (actually Einstein's motivation was on the axle of Fitzgerald contraction; this aim caused to ignore the types of relativity; Einstein preferred to consider the genuine relativity for light's motion).
Whereas an alternative solution (LCS concept) is mentioned for analyzing light kinematics like the simple example which is presented at this topic.
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Is (it) 1.27 million light years or merely 1.27 million years?
Both.
In a vacuum, light travels at "the speed of light".
- So in space, light travels 1 light-year in 1 year.
- And 1.27 million light years in 1.27 million years
If you look at photons emitted now by the Sun and Andromeda, they will pass at the half-way point, which is 1.27 million light years away, in 1.27 million years.
Yes, you are right certainly. Thanks.
In that case, the distance between two photons decreases by a value ' 2 c ' of velocity; or the collision speed is 2c.
In CERN, If the particules accelerate up to big fractions of c; the collision speed can be bigger than ' c '.
The "closing speed" between the particles as measured in the rest frame of the accelerator, can exceed c, however, the relative speed between the particles as measured by either particle cannot equal or exceed c. For example, if both particle A and B have speeds of 0.999c relative to the accelerator, either particle will measure the relative speed between the particles as being 0.999999499c
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V = (v + w) / (1 + v.w/c²) This formula is valid for genuine relativity (If we throw a rocket from/over another rocket; the speed of relative rocket doesn't exceed the value ' c ').
This formula is also valid if you throw two rockets off a single rocket.
Consider that the Earth is one rocket, and the LHC throws two rockets (bunches of protons) in different directions.
Apply this formula, and you will see that the bunches of protons never exceed c compared to the Earth, and they never exceed c relative to each other.
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The velocity addition formula describes how time dilation affects perception in the proper time of a travelling object. It is all to do with relative velocities.
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Two photons (which have been emitted from the Sun and Andromeda on the same moment
"at the same moment" from whose point of view?
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The "closing speed" between the particles as measured in the rest frame of the accelerator, can exceed c, however, the relative speed between the particles as measured by either particle cannot equal or exceed c. For example, if both particle A and B have speeds of 0.999c relative to the accelerator, either particle will measure the relative speed between the particles as being 0.999999499c
Yes, you expressed clearly the nuance.
When the closing speed value exceeds c, an observer (that is located on a particle) cannot determine other particle's simultaneous location because of limited/finite value of light's velocity; and he cannot measure its real relative speed (or decreasing speed of the distance between two objects).
If an observer is an actor of the experiment or analysis; his visual abilities or restrictions causes wrong perception. Therefore we must consider God's eye/sight or the status without observer.
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This formula is also valid if you throw two rockets off a single rocket.
Consider that the Earth is one rocket, and the LHC throws two rockets (bunches of protons) in different directions.
Apply this formula, and you will see that the bunches of protons never exceed c compared to the Earth, and they never exceed c relative to each other.
Yes you can be right; so, if an astronout pushes his shuttle, he moves away from shuttle. However the space shuttle also will move away from astronout by an amount speed toward opposite direction. Both of them get speeds according to LCS/space; arithmetic total of their speeds is the meaning of relative speed according to each one of them and this value cannot exceed c. Please attention: The shuttle and astronout have their own masses; masses and pushing force are the reason of motions.
However, if we realise a photo-flash from shuttle toward opposite direction, the photon packet moves away from a point (that is marked on LCS or space) by the vaue of velocity c . The shuttle had passed over this emitting point at the emitting moment. The distance between the shuttle and photon packet increase by bigger speed than c. The shuttle keeps its motion independently toward anywhere or present orbit. The photon packet goes due to electro-magnetic cycle in space; the shuttle or their source does not cause the motion of photons; so, the "action-reaction" concept is not mentioned.
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The velocity addition formula describes how time dilation affects perception in the proper time of a travelling object. It is all to do with relative velocities.
We have a possibility to use a co-reference frame (The Earth/local places) for mechanic problems. Co-reference frame is useful for analyzing.
We can use similar possibility for light kinematics due to space or virtual/imaginery Light Coordinate System. The velocity of light is already the value c according to space; we can use the universal value of the other actors' speed.
Besides we must not use the observer as an actor in the experiments and analyses.
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Two photons (which have been emitted from the Sun and Andromeda on the same moment
"at the same moment" from whose point of view?
God's sight or theorical imagination.
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Is (it) 1.27 million light years or merely 1.27 million years?
Both.
In a vacuum, light travels at "the speed of light".
- So in space, light travels 1 light-year in 1 year.
- And 1.27 million light years in 1.27 million years
If you look at photons emitted now by the Sun and Andromeda, they will pass at the half-way point, which is 1.27 million light years away, in 1.27 million years.
Some members are insistent about single c for the limit of relative speeds.
If we consider a relativity between an observer and a photon packet of Andromeda, this insistence became valid; but we consider two photon packets that are approaching to each other.
Relativity concept is an alternative method to solve some problems; however this method is unsuccessful for determinig the meeting point (special and classic relativity); meeting point of this method is the inert partner directly.
Realistic/practical/main analyzing method is done by co-reference frame; it does not confuse. If we assign one of test objects as reference frame (inert); we already suppose that its location is fixed; but this is not reality. We use this method for artificial faciliteness.
Please don't fall to a mental trap; you may trust your own intellectual performance.
Of course, Einstein is our an idol/hero (even for me because of the "E = mc² " relation and Bose-Einstein density). However, we can improve our paradigm for cosmological analyses and light kinematics and we can calculate better the age of Universe (my result: 19.28 Gyrs). The mentality of SR prevents cosmological analyses.